1. Field of the Invention
The present invention relates generally to mining machines utilized in longwall mining operations and, more particularly, to an improved drum-cutter mining machine utilizing an auxiliary cutting drum for operating on mined material carried by a conveyor used for supporting the mining machine.
2. Description of the Prior Art
Underground mining operations frequently utilize a mining process referred to as longwall mining in order to most efficiently shear a mineral from a mineral seam.
Longwall mining procedures utilize a drum-cutter mining machine, also referred to as a shearer loader, which is positioned proximate to a mineral seam in a mine wall. The drum-cutter mining machine includes a machine body and cutting drums rotatably supported by support arms extending from opposite ends of the machine body wherein the support arms are pivotally connected to the machine body. The support arms are pivoted about their respective pivotal connections to the machine body in order to position the cutting drums at desired cutting heights. Preferably, a first drum, the leading cutting drum, is positioned to shear an upper portion of the mineral seam, and a second drum, the trailing cutting drum, is positioned to cut a lower portion of the mineral seam along the floor of the mine. By pivoting the respective support arms about their pivotal connections to the machine body, the vertical positioning of the respective cutting drums may be altered. When the mineral is to be sheared from the mine seam, drive motors provide rotational torque to the respective cutting drums. The leading cutting drum thereby shears a first portion of the mine wall, and the trailing cutting drum shears a second portion of the mine wall. The drum-cutter mining machine is translated along the length of the mine seam face upon a longwall conveyor system that includes a rack structure supported by the conveyor and extending along the entire length of the mine wall face. A drive motor in the machine body drives gearing to meshingly engage with individual rack pins of the rack structure to thereby allow translation of the mining machine therealong.
West German Pat. No. 35 27 253 discloses a drum-cutter mining machine equipped with an auxiliary cutting drum. The mining machine is movable along a longwall conveyor. Two support arms pivotally supported by the frame of the mining machine at opposite ends thereof rotatable support cutting drums. The cutting drums are situated on the side of the support arms which face the coal face, and on the opposite side, the goaf side, the cutting drums support drive motors which are connected by gearing to the respective cutting drums for rotation thereof. The cutting drum and the drive motor are arranged on each of the support arms such that the rotational axis of the motor and the rotational axis of the cutting drum are parallel to each other. A jib is pivotally supported on the front free face of the motor. An actuator also extends between the jib and the front face of the motor to impart pivotal movements to the jib. The end of the jib projecting below the drive motor and under the cutting drum carries an auxiliary drum which is drivingly connected by gearing to a butt shaft portion of the motor shaft at the goaf side of the support arm. The connection between the auxiliary drum and the drive motor is formed by a train of gears that extends inside the jib.
Drum-cutter machines used to release coal from thick mine seams are required to operate with cutting drums having large diameters and also provided with drum support arms having a greater length that extends over the radius of the drum. In this way, the drums can be positioned throughout the entire required range of cutting to release material from the thick mine seam. When mining such thick seams, the material loosened by the cutting drums breaks down in large layers which are caught by the conveying elements of the longwall conveyor and pressed against the area of the mining machine bridging the conveyor. This condition leads to jamming, the creation of obstructions and interruptions to working of the mine seam.
The support arms of such a drum-cutter mining machine have a length required to carry the cutting drum through a large pivotal movement in order to cut away coal at the roof of the coal seam while the mining machine travels in one direction, and to cut away coal at the floor of the mine seam through operation of the same cutting drum when the direction of travel by the mining machine is reversed. The drive motor for the cutting drum participates in the pivotal movement of the support arm because it is fastened to the support arm and also carries the jib which is connected thereto as well as the auxiliary drum which is connected to the jib. For this reason, an adjustment device is necessary to constantly bring the jib into a position in which the auxiliary cutting drum can fulfill its function of breaking up portions of debris on the conveyor at the portion of the mining machine bridging the conveyor.
It is accordingly the object of the present invention to provide a mining machine particularly a mining machine constructed for mining thick seams in which an auxiliary cutting drum may be properly positioned without an independent actuator of the drum positioning actuator.